The Bucket Brigade Chip: The Small Secret of Analog Delay

From somewhere in the middle of the 20th century, the world of music saw some drastic changes. This does not come as much of a surprise as these were the times of great technological advancements and cultural revolutions, affecting music in so many different ways, sending this art form into so many new directions. The most notable genre that we got was, of course, rock ‘n’ roll, with the guitar taking a crucial role in this new style.

From the 1950s until now, we’ve seen huge innovations in the world of guitar; from the development of the very first effects pedals, to very delicate and advanced digital guitar modelers. However, despite all the advancements, guitar lovers still tend to praise the good old analog stuff and prefer it over modern digital effects. Some are even ready to pay more for some of those analog effects, just because of the unique tone that they’re producing. It’s something we often see with analog delay/echo effects, with guitar players still desiring the organic and natural tone that these pedals provide. Now, there is a secret to why these pedals sound so great, and it’s the same old ingredient we got to see in older analog delays, those coming from the ’70s and the ’80s. Here, we will be taking a closer look at these pedals and unraveling some secrets about the famous bucket brigade devices and how they made delays sound different.

Bucket brigade devices? What are those?

Bucket brigade devices, or BBD, or analog shift registers, were developed back in 1969 and present discrete-time analog delay lines. By analog delay lines, we mean a line of different electrical components with each of the elements causing a time delay. The analog delay lines saw many different uses, not just for music instrument effects, and the so-called bucket brigade is just one of its forms.

Anyhow, the name of these devices comes from the human chain concept, also known as the bucket brigade, where the transported objects are passed from one person to another, ultimately forming a chain that will help transport bigger quantities from point A to point B. And this is a good analogy for the bucket brigade devices as they consist of a series of capacitors that store the analog signal.

Why bucket brigade devices?

While the 1960s saw some great innovation, achieving effects like echo, flanger or chorus was not that simple. It required those bulky effects devices that used magnetic tape as the storage medium. The development of a small device that would fit into a compact-sized guitar pedal was truly a dream come true. So getting rid of those big units, that would even malfunction regularly, came as a huge relief and the effects pedals manufacturers began implementing BBDs into their new products. These included Boss’ CE-1 and CE-2 choruses, the Ibanez AD-230 analog delay and multi flanger rack unit, Electro-Harmonix Deluxe Memory Man delay, and others.

How does it work and how is it different than digital processing?

Now, explaining all the details about how a bucket brigade device works might take us into some geeky territory; but we’ll try and keep it brief.

So, the BBDs were made as integrated-circuit chips which hold a big number of small capacitors, each of them acting as storage space, or storage “cells.” In addition, a BBD also has switching transistors in it. Basically, the signal is stored in a capacitor and is then passed onto the next capacitor, in the “bucket brigade” manner. The capacitors actually hold a sampled voltage, but in practical terms, you get a stored signal.

The devices can be set to either hold the signal longer in a capacitor or just to transfer them more slowly, which prolongs the delay time. This can be compared to motion pictures with a bunch of frames shown in a certain period of time. And the more samples or frames that you have, the more flow in transitions you will have and the effects will sound clearer.

But since we also have “samples,” something that we usually associate with digital effects, how is an analog delay any different than a digital delay? Well, in a few ways…

First off, digital effects practically “translate” the analog signals into digital information, process it, and then convert it back to analog, changing the information in many different ways during this process. Whereas the analog effects take the exact same copy of the signal voltage at the moment that this copy was made. With the analog devices, like the bucket brigade devices, you have higher fidelity compared to digital effects.

Now, bear in mind that back in the 1980s, when the digital effects were still being developed, this was a pretty big deal. These days, with 24-bit digital encoding, not that many people can make a true distinction between the digital and analog effects. But at the same time, there are those guitar players that do notice these nuances and are pretty strict about using analog delays instead of digital.

There’s also another thing that makes a distinction, aside from the fidelity, and that’s the fact that capacitors in BDDs cannot store the samples as long as the digital effects. The capacitors, in a way, “leak” this information the longer it stays in them, so the information has to be moving quickly to the output. While this might not be a problem for really short delays or flangers, doing a longer delay will result in noticeable fidelity loss.

Just a bit more detail for those who are interested

This is, of course, just a brief explanation of some basic information about how it operates. In addition to all the things explained above, the BBDs have a clock inside of them, enabling them to pass these samples along. The BBDs have two lines in them to pass the signal, with the clock allowing one line to pass one sample at a time. Practically speaking, each of the lines takes a turn, so they are not passing the sample at the same time. The two paths are then mixed together into one and form an output together.

What also needs to be said is that BBDs differ in their capacity. Look at it as if it was a standard RAM memory on each of our personal computers, cell phones, or other devices. Instead of megabytes and gigabytes, we have the so-called “stages” that store the signal. The devices differ in the number of stages and for the purposes of audio effects, they have either 256, 512, 1024, 2048, or 4096 stages. In practical terms, the more stages in a BBD, the more delay time you get for your effect. Everything up to 1024 is often used for flangers or choruses, while the 2048 or 4096 are used for delays.

Creating analog delays brings another challenge with it, as the BBD-based effects are susceptible to unwanted noise. This noise usually comes from clocks or the short distance between each successive sample. There are different ways of tackling these issues, like low pass filtering, gating, companding, output balancing, or treble manipulation.

Analog delay examples

Now that we know some secrets behind how they work, here are some of the analog delay pedals that you can find on the market today.

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